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The human “microbiome”—the trillions of bacteria, yeasts, and other microscopic creatures that live inside a human body—has been one of the major science stories in recent years. It seems that barely a week goes by that we don’t learn something new about the relationship between the human body and the vast population of microbes that call it home.

Despite the pervasiveness of bacteria in our bodies, biologists have long assumed that at least certain parts of it are off limits to foreign organisms. It’s been dogma for more than a century that healthy lungs are sterile—although recent research has shown the microbiome probably extends there, too. And if you were to ask physicians which compartment of the body is least likely to have resident bacteria, most would probably identify the brain: It seems improbable that the central nervous system could function with microbes jumping across the synapses.

Or maybe it could. The PLoS ONE study looked at brain tissue from 10 people, all of whom had either HIV, epilepsy, or some other control disease—and in all 10 samples they found bacterial RNA. The main type of bacteria they found is something called “alpha-proteobacteria,” which is surprising because it’s different from the kinds of microbes researchers have found in adjacent parts of the body like the skin and the nasal passages. This raises the possibility that alpha-proteobacteria is some kind of highly specialized brain bacteria performing an as-of-yet unrecognized function.

While the researchers used tissue samples from subjects suffering from disease, they speculate that all of us are likely to be carrying around ­bacteria in our brains. This study is the first of its kind, and if the results are confirmed, researchers will have a number of provocative questions on their hands: Why are these brain bacteria not harmful? Are they recognized by the immune system and tolerated, or do they somehow fly under the immune radar? And most important of all, what exactly are the bacteria doing in our brains? We consider our thoughts to be the ground zero of our identities, but perhaps even the act of thinking is a team effort.

THE FAST CITY

Italian painter Valerio D’Ospina has created a series of immersive oil paintings of city scenes. D’Ospina, who lives in rural Pennsylvania, calls his series “Urbanscapes.” He uses hard-edged, linear brush strokes and mostly gray-scale colors to create scenes that conjure nostalgia for a grittier, urban past. At the same time, the sense of movement in his paintings and the dramatic perspectives he adopts call to mind something more forward-looking: the city itself racing through history.